Aedus and Xerxes were high templar who held a deep love for each other. Xerxes and Demioch were friends who fought together early in the Great War against the zerg. Aedus and Xerxes merged into a powerful archon early in the war. However, Xerxes "died" when he became part of the archon, and his love for Aedus twisted into bitterness. The combined being fell deeper into self-loathing, existing only to hate and hoping to fall in honorable combat.
Unlike his fellow commanders, Aedus/Xerxes always followed the orders of Syndrea, even when it didn't enjoy them (for instance, destroying the Incubus Brood harvesting operation in the Valley of the Shadow). His actions caused significant damage to the Incubus Brood and drove them into a frenzy, causing them to slaughter many innocent terrans in their rampage. Edullon objected to these heavy handed tactics but was branded as a traitor by Syndrea as a result.
Aedus/Xerxes was given command of Syndrea's vanguard and attacked Edullon and Demioch's forces, along with the terrans that had allied with them. However, despite the element of surprise, the vanguard was defeated, with Edullon killing Aedus/Xerxes in a hand-to-hand duel.